Two-piece potentiometer



Aug. 13, 1968 w, BANG 3,397,374

TWO-PIECE POTENTIOMETER Filed July 6, 1967 INVENTOR. MOGgNS W. BANG3,397,374 TWO-PIECE POTENTIOMETER Mogens W. Bang, Ridgway, Pa., assignorto Stackpole Carbon Company, St. Marys, Pa., a corporation ofPennsylvania Filed July 6, 1967, Ser. No. 651,468 8 Claims. (Cl.338-162) ABSTRACT OF THE DISCLOSURE A substrate supports an electricalresistance element having a curved body with a circular inner edge andlaterally spaced ends, to which electric terminals are connected. Thesubstrate also supports conductive material in the area between acentral opening through the substrate and the space between the ends ofthe resistance element. This material likewise is connected with aterminal. Mounted in the opening is a metal rotor disposed in constantengagement with the adjoining conductive material and carrying anelectric contact engaging the resistance element.

It is among the objects of this invention to provide a potentiometerthat is formed from only two parts, has high power capacity,considerable strength and is very easy and inexpensive to make.

The invention is illustrated in the accompanying drawings in which:

FIG. 1 is a front view of the potentiometer;

FIG. 2 is a rear view;

FIG. 3 is an enlarged central cross section taken on the line IIIIII ofFIG. 1;

FIG. 4 is a front view of a modification; and

FIG. 5 is a detail of a further modification.

Referring to FIGS. 1 and 3 of the drawings, a flat substrate 1 is formedfrom a thin plate of insulating material that preferably is rectangularand has three laterally spaced tongues 2 projecting from one edge. Thissubtrate supports an electrical resistance element 3 that may be formedby applying a coating of resistance material to one side of thesubstrate. The coating preferably is rectangular and spaced a shortdistance from the tongues.

In order to form a resistance path along the resistance material, thereis a circular gap 5 in the coating. The gap extends from one edge of thesubstrate at a point between the central tongue and one of the outertongues and around to the same edge at a point between the centraltongue and the remaining tongue. The curved portion of the resistancematerial outside of a gap forms the resistance element that will beengaged by a sliding contact. Although the outside as well as the insideof the resistance element may be curved, it is preferred that theoutside be rectangular as shown because it provides a greater area ofresistance material for heat dissipation and thus increases the wattagerating of the element. The gap 5 can be formed in different ways. Oneway is to form a circular groove 6 (FIG. 3) in the substrate before theresistance material is applied. During application of that material,care is taken to prevent it from bridging the groove, so a gap is leftin the coating. The two outer tongues are covered with metal coatings 7that are joined to the ends of the resistance element to form electricterminals for it. The center tongue likewise is coated with metal toform a terminal, but this coating 8 extends inwardly between the ends ofgap 5 and a short distance into the area encircled by the gap.

The substrate and its resistance coating are provided with an opening 10therethrough concentric with the circular gap. This opening positionsand retains a rotor 11 that carries a contact 12 that is slidable alongthe resistance element outside of the gap and onto the inner ends of theend terminals. The rotor is formed from a single piece of sheet metal,the central portion of which may be provided with several struck-outtongues 13 which, as shown in FIG. 2, are bent back through opening 10and then outwardly to overlie the rear surface of the substrate. Or, asshown in FIG. 5, the ends of the tongues may be provided with humps .14that snap out over the rear edge of opening 10 when the tongues areinserted. In either case, the tongues engage the side wall of theopening to prevent lateral movement of the rotor, and the ends of thetongues hold the rotor in the substrate. The rotor is large enough indiameter for a portion of it to be in constant engagement with the metalcoating 8 inside the area encircled by the circular gap.

It has been found that the pressure of the rotor against metal coating 8is more uniform if the rotor is provided with a plurality ofcircumferentially spaced fingers 15 radiating from its center. Eachfinger forms a spring finger, some of which engage the resistancematerial encircled by the gap and one or more of which always engagesthe metal coating 8. For smoother operation, the outer end of eachfinger is provided with a pressed-out nib 16. One of the fingers islonger than the others and extends out across the gap 5 for engagementwith the resistance element around the gap. The outer end of this finger12 has a pressed-out nib 17 for engaging the resistance element.

It will be seen that the rotor can be turned in either direction fareough for its contact to slide off the resistance element and onto theinner end of one of the outer terminals. To indicate that the contactshould be turned no further, each of these terminals may be providedwith a stop of any suitable form. For example, the stop may be a recess,such as a hole 20, into which nib 17 will snap when it reaches the hole.The rotor can be turned by any suitable instrument, such as a screwdriver, inserted in the slots formed by its struck-out tongues.

This potentiometer is easy and inexpensive to make because it is formedfrom only two pieces, i.e., the coated substrate and the metal rotorwith its integral tongues and contact, which can be assembled quickly.There are no separate contacts nor fastening members. The two pieces areinexpensive to make and a simple bending operation or snap actionfastens them together. Furthermore, due to its particular construction,this potentiometer gs very thin and can be used in areas that are quiteconned.

In the modification shown in FIG. 4, the gap is formed by a ridge 22 onthe substrate 23 from the top of which the resistance coating 24 hasbeen removed by grinding or some other suitable action. Also, thesliding contact of the rotor 25, instead of being the outer end of along straight spring finger, is a loop 26, the ends of which areintegral with the rotor between some of its spring fingers 27.Otherwise, this potentiometer is the same as the one first described andhas the same advantages.

According to the provisions of the patent statutes, I have explained theprinciple of my invention and have illustrated and described what I nowconsider to represent its best embodiment. However, I desire to have itunderstood that, within the scope of the appended claims, the inventionmay be practiced otherwise than as specifically illustrated anddescribed.

I claim:

1. A potentiometer comprising a substrate, a coating of resistancematerial thereon, three integral tongues projecting from one edge of thesubstrate, said coating having a gap therein extending inwardly fromsaid edge of the substrate between the center tongue and one of theouter tongues and around in a circle to said edge between the centertongue and the remaining tongue to form a resistance element around theoutside of the gap, conductive material on the two outer tongues joinedwith the ends of said resistance element, conductive material on thecenter tongue and extending between the ends of said gap into the areaencircled by the gap, the substrate being provided with an openingthrough it and said coating concentric with said gap, a metal rotorrotatably mounted in said opening and disposed in constant engagementwith the conductive material in said area, and an electric contactcarried by said rotor and electrically connected therewith, the contactengaging said resistance element and being movable along it by therotor.

2. A potentiometer according to claim 1, in which the portion of thesubstrate supporting said resistance coating is rectangular and theresistance coating substantially covers one side of said portion exceptfor said gap and opening.

3. A potentiometer according to claim 1, in which said resistancecoating joins said conductive material along a substantially straightline extending across the substrate between said opening and tongues.

4. A potentiometer according to claim 1, in which said rotor has aplurality of circumferentially spaced fingers radiating from its centertoward said gap, the outer end of at least one of the fingers alwaysengaging said conductive material in said area as the rotor is turned.

5. A potentiometer according to claim 1, in which said rotor is a singlepiece of sheet metal provided centrally with struck-out tongues bentthrough said opening and engaging the side wall thereof, the free endsof the tongues being shaped to overlap the edge of said opening remotefrom said resistance element to connect the rotor to the substrate, andthe openings in the center of the rotor created by said tongues forminga slot to receive a tool for turning the rotor.

6. A potentiometer according to claim 1, in which said gap is formedfrom a ridge projecting from the surface of the substrate, with the topof the ridge free of said resistance coating.

7. A potentiometer according to claim 1, in which said contact has aprojection on one side slidable against the resistance element, and saidsubstrate is provided with a recess near each end of said element forreceiving said projection to limit movement of the contact.

8. A potentiometer comprising a substrate having a rectangular portionand three laterally spaced tongues projecting from one edge, anelectrical resistance element on said rectangular portion having acurved body with a circular inner edge between laterally spaced ends,said element extending outwardly from said inner edge substantially tothree contiguous edges of said rectangular portion of the substrate, thesubstrate being provided with an opening therethrough concentric withsaid circular edge, conductive material on said tongues and extendinginwardly into the area encircled by the resistance element and also intocontact with said element ends, the inner edge of said conductivematerial extending in a straight line across the substrate, a metalrotor rotatably mounted in said opening and disposed in constantengagement with the conductive material in said area, and an electriccontact carried by said rotor and electrically connected therewith, thecontact engaging said resistance element and movable along it by therotor.

References Cited UNITED STATES PATENTS 1,881,446 10/1932 Flanzer 338-1623,201,737 8/1965 Mathison.

FOREIGN PATENTS 1,03 6,986 8/ 1958 Germany. 1,135,557 8/1962 Germany.1,318,659 8/1963 France.

ROBERT K. SCHAEFER, Primary Examiner.

H. I. HOHAUSER, Assistant Examiner.

